‘56 Up” is as good a point as any to get hooked on the magnificent half-century series of documentaries, beginning in 1964 with “7 Up,” that has explored the lives of a group of British citizens with a level of depth and insight unheard of in this medium — or perhaps any.

New episodes of the documentary air every seven years on television in the UK, where each participant is a celebrity — one of them recalls being asked for an autograph when astronaut Buzz Aldrin was standing next to him. The films shift back and forth in time with clips from previous editions to remind us who these people were as children, as young adults and in early middle age.

Now, most of them — ranging on the socioeconomic spectrum from prep-school grads to products of orphanages — are grandparents. And director and narrator Michael Apted is able to get them to reflect on their lives to such a degree that you may get to know these people better than anyone you know. Except for your inner circle.

The purpose of the series was to prove Britain’s widely held assumption of class determinism — you are what you are born into — but the reality is more complicated. Symon, for instance, the only child of color portrayed here (he was given up to a children’s home in shame after being born out of wedlock) and one who had five kids of his own before he was 30, turned out to be a blue-collar worker as you might expect. Yet he blames his laziness for his lack of economic success, even as he seems to be one of the more content of the group. On the other hand, two posh boys who even at age 7 were pretentious little twits, did indeed become rich lawyers. One of them protests that his dad died when he was 9, and that his hardworking mother and a scholarship are the reasons he was able to graduate from Oxford.

The film is far too rich to be reduced to banal talking points, though. It encourages conversation about what Apted’s gang has learned (or should have learned) about family, ambition, education and the role of the state. One woman, who has arthritis but seems fairly able, has lived on disability checks for more than 14 years. She protests angrily that (as she has recently been ruled fit to work) she’ll take a job if, and only if, the prime minister of the country finds her one — a shocking illustration of how a government that seeks to comfort all simply builds ever-increasing dependency.

Perhaps Apted’s most fascinating case is Neil, who is obviously very bright — but was not quite bright enough to get into Oxford — and suffers from an unspecified “nervous complaint.” After spending much of his life homeless and wandering, he has at age 56 arrived at what looks like a happy ending. Well, sort of: He’s a local politician.